It is known that a block copolymer can be obtained by an anionic copolymerization of a conjugated diene compound and an alkenyl arene compound by using an organic alkali metal initiator. Block copolymers have been produced which comprise primarily those having a general structure EQU A--B and A--B--A
wherein the polymer blocks A comprise thermoplastic polymer blocks of alkenyl arenes such as polystyrene, while block B is a polymer block of a selectively hydrogenated conjugated diene. The proportion of the thermoplastic blocks to the elastomeric polymer block and the relative molecular weights of each of these blocks is balanced to obtain a rubber having unique performance characteristics. When the content of the alkenyl arene is small, the produced block copolymer is a so-called thermoplastic rubber. In such a rubber, the blocks A are thermodynamically incompatible with the blocks B resulting in a rubber consisting of two phases; a continuous elastomeric phase (blocks B) and a basically discontinuous hard, glass-like plastic phase (blocks A) called domains. Since the A--B--A block copolymers have two A blocks separated by a B block, domain formation results in effectively locking the B blocks and their inherent entanglements in place by the A blocks and forming a network structure.
These domains act as physical crosslinks anchoring the ends of many block copolymer chains. Such a phenomena allows the A--B--A rubber to behave like a conventionally vulcanized rubber in the unvulcanized state and is applicable for various uses. For example, these network forming polymers are applicable for uses such as moldings of shoe sole, etc.; impact modifier for polystyrene resins and engineering thermoplastics; in adhesive and binder formulations; modification of asphalt; etc.
Conversely, as the A--B block copolymers have only one A block, domain formation of the A blocks does not lock in the B blocks and their inherent entanglements. Moreover, when the alkenyl arene content is small resulting in a continuous elastomeric B phase. The strength of such polymers is derived primarily from the inherent entanglements of the various B blocks therein and to a lesser extent the inherent entanglements of the A blocks therein. However, the non-network forming polymers have found particular utility as viscosity index improvers (U.S. Pat. Nos. 3,700,748; 3,763,044; 3,772,196; 3,965,019; and 4,036,910). Non-network forming polymers are also utilized in adhesive and binder formulations and as modifiers or plasticizers for polystyrene resins and engineering thermoplastics (U.S. Pat. No. 4,584,338).
Network forming copolymers with a high alkenyl arene compound content, such as more than 70% by weight, provide a resin possessing both excellent impact resistance and transparency, and such a resin is widely used in the field of packaging. Many proposals have been made on processes for the preparation of these types of block copolymers (U.S. Pat. No. 3,639,517).
Both the network forming (A--B--A) and non-network forming (A--B) polymers are physically crosslinked, these polymers may be handled in thermoplastic forming equipment and are soluble in a variety of relatively low cost solvents.
While in general these block copolymers have a number of outstanding technical advantages, one of their principal limitations lies in their sensitivity to oxidation. This behavior is due to the unsaturation present in the elastomeric section comprising the polymeric diene block. Oxidation may be minimized by selectively hydrogenating the copolymer in the diene block, for example, as disclosed in U.S. Pat. No. Re. 27,145 and the above referenced VI improver patents. For example, prior to hydrogenation, the block copolymers have an A--B or an A--B--A molecular structure wherein each of the A's is an alkenyl-arene polymer block and B is a conjugated diene polymer block, such as an isoprene polymer block or a butadiene polymer block preferably containing 35-55 mole percent of the condensed butadiene units in a 1,2 configuration.
Non-network forming (A--B) block copolymers are especially deficient in applications in which good mechanical integrity and deformation resistance are required. This behavior is a consequence of the lack of inherent entanglements of the various B rubber blocks and to a lesser extent the entanglements of the A blocks therein which controls strength under tensile deformation. Additionally, these non-network forming copolymers, in particular A--B copolymers, are also deficient in viscosity index (VI) improver applications wherein thickening efficiency is lost at higher temperatures. As such, improvement in such properties may be achieved by enhancing the integrity of the alkenyl arene domains and the elastomeric matrix through the incorporation of interacting functional groups along the polymer chain.
Conversely, network forming copolymers are known to have particularly high tensile strengths at room temperature due to the formation of glassy phase arene block domains which act as physical crosslinks locking in the inherent entanglements within the rubbery B block matrix. The mechanical integrity of these domains and the resulting network structure formed appear to control the tensile strengths of these copolymers. Moreover, at elevated temperatures, the mechanical integrity of block copolymers is limited to the integrity of the hard phase arene block domains. For example, network forming copolymers having arene blocks of polystyrene have poor mechanical properties at high temperature which may be attributed to the weakening of the polystyrene domains above its glass transition temperature (Tg) of 100.degree. C. Improvements in the high temperature characteristics of the network forming block copolymers may be achieved by enhancing the integrity of the alkenyl arene domains to higher temperatures.
These selectively hydrogenated block copolymers are further deficient in many applications in which interactions are required between it and other materials. Applications in which improvements in adhesion characteristics may promote improved performance include (1) the toughening of, and dispersion in, polar polymers such as the engineering thermoplastics; (2) the adhesion to high energy substrates in a hydrogenated block copolymer elastomer based high temperature adhesive, sealant or coating materials; and (3) the use of hydrogenated elastomers in reinforced polymer systems. The placement of functional groups onto the block copolymer may provide interactions not possible with hydrocarbon polymers and, hence, may extend the range of applicability of this material.
Many attempts have been made to improve the impact properties of polyamides by adding low modulus modifiers which contain polar moieties as a result of polymerization or which have been modified to contain polar moieties by various grafting techniques. To this end, various compositions have been proposed utilizing such modifiers having nitrogen containing functional groups thereon, for example, Epstein in U.S. Pat. No. 4,174,358, Hergenrother et al. in U.S. Pat. No. 4,427,828; and Beever et al. in U.S. Pat. No. 4,588,756.
Epstein discloses a broad range of low modulus polyamide modifiers which have been prepared by free radical copolymerization of specific monomers with acid containing monomers. Alternatively, Epstein discloses the modification of polymers by grafting thereto specific carboxylic acid containing monomers. The grafting techniques allowed for therein are limited to thermal addition (ene reaction) and to nitrene insertion into C--H bonds or addition to C.dbd.C bonds (ethylenic unsaturation). Via these grafting techniques, Epstein may produce modifiers with nitrogen-containing functional groups. With nitrene insertion, the aromatic sulfonyl azides utilized therein are used as a means for grafting a carboxylic acid group onto the modifier. As such, the interaction between the polyamide and the modifier is achieved via the carboxylic acid group of these nitrogen containing functional groups. On the otherhand, when a dicarboxylic acid or derivative thereof (e.g., an anhydride) group is grafted thereon say via thermal addition, the dicarboxylic acid group may either directly interact with the polyamide via a grafting reaction or indirectly interact with the polyamide by first further modifying the dicarboxylic acid group by reacting same with a caprolactam to form a cyclic imide with a pendant polyamide oligomer chain which in turn acts as a compatibilizer with the polyamide or possible transamidation graft site.
Though Epstein does disclose a broad range of polyamide modifiers, Epstein does not disclose or suggest the utilization of hydrogenated copolymers of alkenyl arenes and conjugated dienes nor, more particularly, modified selectively hydrogenated copolymers of alkenyl arenes and conjugated dienes as polyamide modifiers. Furthermore, Epstein relies upon the carboxylic acid portion, as opposed to the nitrogen portion, of the functional groups in the modifiers therein as the active participant in the impact modification of the polyamide.
Hergenrother et al. disclose polyamide compositions which contain a modified partially hydrogenated aromatic vinyl compound/conjugated diene block copolymer as a polyamide modifier. In order to improve the weatherability and resistance to heat aging, Hergenrother et al. partially hydrogenate the block copolymer in their respective blends to an ethylenic unsaturation degree not exceeding 20 percent of the ethylenic unsaturation contained in the block copolymer prior to hydrogenation. Once the block copolymer is partially hydrogenated, the block copolymer is modified by grafting a dicarboxylic acid group or derivative thereof (e.g. anhydride moieties). Hergenrother et al. disclose grafting via thermal addition (ene reaction) utilizing the available residual unsaturation in the block copolymer. As such, Hergenrother et al. retained the deficiencies associated with the reversibility of the ene reaction. The anhydride moieties therein, like in Epstein, are believed to undergo a grafting reaction with the terminal amines of the polyamide to form a cyclic imide, thereby converting the functional group into a nitrogen-containing functional group. However, it is readily apparent that Hergenrother et al. place heavy reliance on these anhydride moieties, as opposed to a nitrogen-containing functional group, to effect the impact modification of the polyamide.
As is readily apparent from the foregoing prior art polyamide compositions utilizing alkenyl arene/conjugated diene block copolymers as polyamide modifiers, improved impact modification of the particular polyamide is achieved via specific interactions, between the modified diene block and the polyamide. Thus, to the extent that impact modification and strength mechanisms rely on the elastomeric properties of the diene block of the copolymer, these properties have been adversely affected by modifying the diene block in this manner.
Beever discloses a polyamide composition containing an oil-soluble organonitrogen compound grafted hydrogenated conjugated diene/monovinylarene copolymer, such as those described in U.S. Pat. No. 4,145,298 to Trepka. The copolymer is characterized as having been prepared by the process which comprises (1) metalating a hydrogenated conjugated diene hydrocarbon/mono vinylarene hydrocarbon copolymer and (2) reacting the resulting metalated hydrogenated copolymer with effective amounts of at least one nitrogen-containing organic compound, thereby preparing the grafted copolymer. The suitable nitrogen containing organic compound are specifically described by the general formula: EQU X--Q--(NR.sub.2.sup.3).sub.n or Y--Q--(NR.sub.2.sup.3).sub.n ].sub.m
wherein each R.sub.2.sup.3 is the same or different alkyl, cycloalkyl, aryl, or combination thereof, Q is a hydrocarbon radical having a valence of n+1 and is a saturated aliphatic, saturated cycloaliphatic, or aromatic radical, or combination thereof, X is a functional group capable of reacting on a one-to-one basis with one equivalent of polymer lithium, Y is or contains a functional group capable of reacting on a one-to-one basis with one equivalent of polymer lithium, n is at least one, and m is 2 or 3. X includes: ##STR1## wherein R.sup.4 is hydrogen, or an alkyl, cycloalkyl, or aryl radical or combination radical; N.tbd.C--; and R.sup.3 N.dbd.CH--. Thus, it is readily apparent that suitable nitrogen-containing organic compounds therein are electrophilic graftable molecules requiring three portions: (1) X, a lithium reactive functional group; (2) NR.sub.2.sup.3, the nitrogen containing portion of the molecule (a tertiary amine); and (3) Q, which couple together X and NR.sub.2.sup.3. This method of using an electrophilic graftable molecule having an appended amine site as a route to attach amine groups to the block copolymer suffers from the disadvantage that the product of the reaction of X with the lithiated polymer is itself a functional site (a ketone or alcohol for example). The introduction of this second (reactive) site of functionality (with the amine being the other site of functionality) may lead to undesirable effects particularly in the process of incorporating the required amine functionality.
With respect to viscosity index improvers, many attempts have been made to improve the viscosity index of lubricants and the like by adding modifiers, which contain polar moieties as a result of various grafting techniques. The incorporation of nitrogen-containing functional groups onto the modifiers imparts thereto dispersant characteristics in lubricants, fuels and the like. To this end, various viscosity index improver/dispersant modifiers have been proposed having nitrogen-containing functional groups thereon, for example, Kiovsky in G.B. Pat. No. 1,548,464, Hayashi et al. in U.S. Pat. No. 4,670,173, and Trepka in U.S. Pat. Nos. 4,145,298 and 4,328,202.
Both Kiovsky and Hayashi et al. disclose a partially or selectively hydrogenated aromatic vinyl compound/conjugated diene block copolymers to which has been grafted a carboxylic acid group (or anhydride thereof) onto the diene portions of the polymer. The graft is effected via a free radially initiated reaction. Once modified with carboxyl functional groups, the modified polymer is further modified by reacting these carboxyl-functional groups with an amine containing material, e.g. a mono- or polyamine. The so modified polymer contains a nitrogen-containing functional group to impart dispersancy characteristics thereto.
Trepka discloses an oil-soluble organonitrogen compound grafted hydrogenated conjugated diene/monovinylarene copolymer. This same polymer is utilized to impact modify polyamides by Beever et al. in U.S. Pat. No. 4,588,756, previously discussed herein. The disadvantage of utilizing such a polymer for impact modifying polyamides are equally applicable with respect to viscosity index improver and dispersant applications. Of particular importance is the disadvantage related to the introduction of a second (reactive) side of functionality (a ketone or alcohol for example) with the amine being the other site of functionality. This second functional site is particularly susceptible to oxidative attack and cleavage of the amine functional group from the polymer, particularly under the severe conditions encountered in an internal combustion engine. Such an occurrence would be expected to significantly reduce the dispersant activity of the polymer.
On the other hand, the present invention relates to a thermally stable, modified, selectively hydrogenated conjugated diene/alkenyl arene copolymer grafted with at least one functional group utilizing the metalation process. Herein, the functional groups are amide functional groups which are grafted primarily in the alkenyl arene portions of the copolymer. The introduction of a second site of functionality is avoided by utilizing electrophiles, as opposed to electrophilic graftable molecules such as in Beever. The electrophiles are isocyanates which become amide functional groups upon reacting with the lithiated polymer and quenching with a proton source; alternatively, the lithiated polymer is reacted with the electrophile carbon dioxide and the resulting carboxylic acid functionalized block copolymer is reacted with a primary or secondary amine and heated to become amide functional groups.